Originally Posted by shadyJ
The vented subs which are totally free from port chuffing would have to be tuned pretty high, higher than most in this message board would care for.
There are two primary attributes of a port: diameter, length.
At a given tuning frequency, X, a Y diameter port must be Z length.
Chuffing happens when the speed of the air within a port structure is sufficient enough to cause turbulence.
Say you had a subwoofer tuned to 20hz with a 1inch diamter port that chuffed enough to be unsatisfactory. What this really means is that at some frequency and gain the speed of the air in the port is too high. The primary way to lower the air speed in a port is (other than just turning it down) actually to increase Y, it's diameter. The only problem is that as Y diameter increases.... Z length increases obnoxiously.
You can make most ports chuff pretty easy, regardless of their tuning values. Put enough gain through the driver, move enough air, it'll chuff. No port is immune. Again, the primary way to get around this though is increased port diameter, but again doing this makes port length also increase obnoxiously.
So, what this means is that you need to come to a compromise in the overall enclosure. Normally that compromise is space consumed by the subwoofer, so boxes get smaller and ports get smaller. This is all fine and good as long as you don't get into the gain enough to cause the ports to chuff.
Get into a higher powered sub solution and want to keep that insane depth-diving low frequency response without chuffing ports? Bigger ports. Much longer ports. Bigger net enclosure size.
This is indeed the primary reason I went with the Hsu design. It's an absolutely huge box (especially if you're used to big box store subs), with two massive ports that can be used one at a time or concurrently. Both ports are the same diameter and length, so what that means is you can choose between frequency tunings of the box (and you should select the appropriate, supported, equalization settings with your port config).
With both ports open you've got a lot of room to breath, the tuning has gone up (22hz), and you'll need a lot of gain to pump through it before it'll chuff. I've personally never made mine chuff, though I know I could. That's more gain than I want to deal with in my room. Pictures would come off walls.
With one port open, you're cutting the breathing space in half, dropping the tuning down to 16hz... here settings are more potentially chuffy. Tones played at and around the tuning frequency are going to push the most air through the port, and there's less port cross section to allow airflow, ergo air speed goes up. Even here... before I've ever made it to chuffville I'm already flexing the drywall in the walls and ceiling and causing bodily discomfort.
Sorry for the ramble. I spent this weekend finishing up an enclosure experiment and have ports on the brain. For the record, .24 cubic feet tuned to 60hz with 1/2 inch diameter and 3/4 inch long ports doesn't chuff at tune with 15 watts going through a couple of full range 4's.